Fuse and method of manufacture



Sept. 14, 1965 s. A. BERTHEL ETAL 3,206,579

FUSE AND METHOD OF MANUFACTURE Filed Feb. 27. 1961 1ap 1@@ 46a ,14 all16a 12 16a 12a 1 1 22 H Li: 0% m B FRED I SCH/I'FMACHER 122 B) ATTORNEYUnited States Patent 3,206,579 FUSE AND METHOD OF MANUFACTURE GustAlbert Berthel, Park Ridge, Ill., and Fred J. Scliitfmacher, Winchester,Mass, assignors to Federal Pacific Electric Company, a corporation ofDelaware Filed Feb. 27, 1961, Ser. No. 91,834 6 Claims. (Cl. 200-123)The present invention relates to electrical fuses and to methods of fusemanufacture.

It has for long been recognized that dual-element fuses have highlydesirable characteristics for providing fastblowing operation undershort-circuit conditions and delayed blowing under conditions ofmoderate but persistent overload. Common, widespread use of such fuseshas been deterred by relative high cost, due to their construction andthe methods used to make them.

Ideally, dual-element fuses include a fuse link having a region ofrestricted cross-section that blows almost instantly in response to ashort-circuit, and a body of lowmelting alloy as a series conductorwhich melts and clears the circuit under conditions of prolongedmoderate overload. An object of the present invention resides in theprovision of a fuse of novel construction having such characteristicsyet which is suited to economical manu facture so as to encourage wideruse of dual-element fuses.

In an effort to simulate dual-element fuse characteristics withoutresorting to complicated construction and costly manufacturing methods,fuses have been made in which a strip of metal of a relatively highmelting-point metal is formed with a local constriction, and a body oflow-melting alloy is mounted on the strip adjacent to the constriction.The theory of operation of such fuses is that the alloy material acts asa heat sink to absorb heat developed by moderate overload currentthrough the fuse. The current tends to raise the temperature of thestrip primarily at the constriction. It is considered that, when thetemperature rises to the melting point of the alloy, the melted alloymetal drops off and the temperature of the strip rises rapidly at theconstriction until the fuse blows,

This type of simulated dual-element fuserecommends itself largelybecause of its low cost and by its seeming near approach to truedual-element fuse characteristics. However, on closer consideration itbecomes clear that it has serious short-comings. The final phase ofdelayedblowing operation of such a fuse necessitates a temperature risesuflicient to melt the high-melting strip of metal. This contrasts withthe moderate temperature prevailing I at the instant of blowing of atrue dual-element fuse,

which occurs virtually at the instant when the alloy melts and dropsoff. Moreover there is a relatively wide latitude of inconsistentblowing times among simulated dualelement fuses of the same design inresponse to a given level of moderate overload current. Suchinconsistent blowing times interferes with accuracy in ratings of suchfuses.

An excessive temperature rise in a fuse has a number of undesirableconsequences. Sometimes the end of the fuse link becomes so hot near oneof the fuse terminals that the solder connection at that point opens.fuse looks like a good one when inspected at the usual window. In suchcases, it is difficult to locate the blown fuse among several good onesin a service enclosure. Further, the excessive temperature rise involvedin the operation of such a fuse inevitably involves higher temperaturesin the fuse box than would prevail with true dual-element fuses.

Accordingly, an object of the present invention resides in novelfeatures of construction of dual-element fuses that are economical tomanufacture and yet which have attractive characteristics oflow-temperature rise when Such a margin.

blowing occurs in response to moderate overloads; of open-circuitingreliably at the region where the alloy body is mounted; and ofresponding to given levels of moderate, prolonged overload by blowingafter delay times that are consistent for any given level of moderateoverload, within a comparatively narrow range of delay times.

A further feature of construction of the novel dualelement fuse residesin the utilization of the delay-element alloy body as a rating indicatorexposed to view at a window in the fuse enclosure. This feature providesmaximum assurance against possible error in manufacture, due to thewrong size link being assembled into a fuse body whose label might notmatch the true rating of the fuse link.

A still further object of the invention resides in a fuse link in whicha strip of fuse-link metal of moderate length is arranged to have anextended-area joint to the alloy body. This feature minimizes thepossibility of contact resistance at the joint introducing an uncertainheating factor. Any uncertainty due to the joint resistance entering asa significant factor would cause blowing of the fuse at a current lowerthan its rating by an uncertain For this reason, the provision of alarge joint area (disproportionately large when compared to the Width ofthe strip) minimizes the possibility of joint resistance entering intothe fuse characteristic as a significant and erratic factor.

Still further objects of the invention reside in novel methods ofmanufacture of fuses, for attaining the foregoing operatingcharacteristics while at the same time achieving low unit costs.

In carrying out the foregoing objects, a fuse link is prepared bydividing a band of relatively high melting-temperature metal intoendwise aligned strips having elongated projecting mutually spacedportions and integral interconnecting portions; joining a body oflow-melting alloy to the elongated portions; and removing the integralinterconnecting portions that join the strips. This is done, in thespecifically disclosed embodiments below, by cutting away theinterconnecting portions outside the area that are joined to the body,leaving the low-melting alloy body as the only current path between thestrips.

The alloy body is relatively large and massive (depending, naturally, onthe current rating of the fuse) and will consistently melt and drop awaywhenever there is a persistent moderate overload. Consequently, bydisposing the alloy body near the fuse window, a correspond inglyreliable indicator is provided for evidencing the condition of the fuse.Further, by embossing or otherwise applying a rating label to the alloybody, the best possible safeguard is provided to assure correctness ofthe rating label. There can be no error that might otherwise result frommounting an unlabeled fuse link of "one rating in an enclosure bearing adifferent rating label.

The nature of this invention and its further features, objects andadvantages will be more fully appreciated from the following detaileddescription of two illustrative embodiments which are shown in theaccompanying drawings.

In the drawings:

FIGS. 1 to 3 show progressive phases of manufacture of a fuse link,somewhat enlarged, according to one embodiment of the invention; 7

FIG. 3A is a cross-section viewed from the line 3A-3A in FIG. 3;

FIG. 4 illustrates the fuse link at the stage in FIG. 3 but viewededgewise and being subjected to a heating operation;

FIG. 5 illustrates a further phase in the manufacture of the fuse link;and

FIG. 6 is an enlarged cross-section of a completed fuse.

FIG. 7 is a view like that of FIG. 5, illustrating another embodiment ofthe novel construction and manufacturing methods, having certain novelfeatures in common with the embodiment in FIGS. 1-6.

Referring now to FIGS. l6 and, particularly to FIG. 1, a band of metalsuch as copper is shown, in its condition following an initial piercingoperation. In this operation, slot 12 is cut and holes 14 are punched.Slot 12 has extensions 12a alongside holes 14. This slot divides thecontinuous band of copper into pairs of strips 18a and 18b at the endsof each slot 12, interconnected by portions 16a and 16b. It will beunderstood that many slots 12 are formed in spaced sequence along acontinuous supply of copper band in making a series of fuse linksautomatically, using automatic machinery. Attention is directed to thesingle illustrated fuse link of the series as it progresses through asequence of manufacturing operations.

In the next step, areas 16a, 16b and 20 are tinned as shown in FIG. 2. Ashort length 22 is next cut from a strip of usual low-melting fuse alloymetal used in dualelement fuses, and body 22 is sharply bent or formedand assembled as shown across portions 16:: and 16b of the band 10. Body22, as indicated in the drawing, is relatively massive in contrast tothe strips 18a and 18b and particularly in contrast to the regions ofconstricted crosssection flanking holes 18. The width of strip used forforming body 22 is preferably a bit smaller than the length of slot 12disregarding extensions 12a.

Tools A apply pressure to body 22 as shown in FIG. 4, squeezing itagainst portions 16a and 16b of band 10. At the same time, a controlledcurrent impulse from source B is delivered by conductive jaws C andthrough switching device D so as to develop enough heat to form a goodsoldered joint between each interconnecting portion 16a and 16b and boththe top and bottom layer of body 22. This heating operation may besupplemented by heating body 22 with controlled current deliveredthrough tools A and B. It will be appreciated that this manner offorming and connecting or uniting body 22 to portions 16a and 16b asillustrated is presently preferred, but that body 22 may alternativelybe applied in a casting operation. The conditions are such that a goodmetal-tometal union is formed between the opposed areas of body 12 andportions 16a and 1611 used herein the terms connection and joint referto such union and not to a mere mechanical fastening.

Body 22 is embossed with indicia 23, the numerals 30 in FIG.representing a SO-ampere rating. Pieces of copper 24 are cut from theband so as to leave a tongue 16a extending integrally from strip 18a andto leave another tongue 16b extending integrally from strip 18b. Thesestrips are thus electrically interconnected only by alloy body 22.Tongues 16a and 16b are accurately spaced apart and are disposedlaterally opposite each other, edgewise. The removal of pieces 24 iseffected without removing and wasting any of the alloy and withoutinterference from body 22, an operation that is made possible by theslot 12 extending outside the alloy body.

An individual fuse link is cut from the continuous series formed asdescribed in connection with FIGS. 1-5. It is formed into the shapeillustrated in FIG. 6, to be received in the plug-free enclosurenaturally and without any stress that could bias the two strips 18a and18b toward each other. The plug fuse enclosure shown includes aporcelain, glass or other suitable insulating body 26, an end terminal28, a screw terminal 30 and a window 32 as of mica held across the topof body 26 by ferrule 34.

The embossed indicia 23 of body 22 are disposed reasonably close towindow 32. The ends of strips 18a and 181') are soldered to terminals 28and 30, respectively, using a higher-melting alloy than that of body 22.

The fuse shown in FIG. 6 and made as described has a number of importantadvantages. It is of elementally simple construction while retainingdesirable properties and characteristics of true dual-element fuses.When a sudden extreme overload occurs, blowing takes place at one of theholes 14 that is opposite window 32. In the event of a moderate butpersistent overload, the temperature rise needed to blow the fuse isonly that required to melt the alloy body 22. As soon as it melts, itdrops and leaves an open gap between tongues 16a and 16b. There is noneed to melt any part of the copper in the fuse link. This constructionis remarkably consistent in its overload time-current characteristic,among many fuses made in the same manufacturing operations, in contrastto fuses intended to simulate dual-element fuse characteristics but inwhich the alloy body is not electrically a series part of the fuse link.

When blowing occurs, the event is reliably displayed at the windowbeause blowing of the novel fuse occurs with a high degree of uniformity(among many like fuses) at the intended region of the link. It is ofcourse usual to expect the window to reveal any blown fuse, butunfortunately fuses may become open-circuited at other joints. This aparticular problem in fuses where higher temperatures are reached priorto blowing, in which case the break in the circuit may develop at asoldered terminal so as not to be displayed at the window. Such atroublesome occurrence is virtually eliminated by the fuse constructiondescribed.

A modification is illustrated in FIG. 7, which is most nearly comparableto FIG. 5. Reference numerals in the IOO-series are used in FIG. 7 todesignate parts corresponding to like parts in FIG. 5.

Tongues 116a and Heb extend from strips 118a and 118b, and regions ofconstricted cross-section are created by pierced holes 114. When thefuse link is being made, strips 118a and 11811 are interconnected andtongues 116a and 116]) are fixed in relation to each other by narrowmarginal bridging portions represented in broken lines. After body 122has been united to tongues 116a and 11612, these bridging portions 124are cut away in an operation that occurs wholly outside the body 122.

As will be apparent, this embodiment utilizes variations of the novelfeatures of the embodiment in FIGS. 1-6. When assembled into an enlosuresuch as that in FIG. 6, it achieves many of the purposes of the firstembodiment.

It will be appreciated that the foregoing embodiments of the inventionin its various aspects are susceptible to detailed modification andvaried application of the features of novelty, and consequently theinvention should be broadly construed in accordance with its full spiritand scope.

What is claimed is:

1. A dual-element fuse link including first and second relatively longstrips of metal each having an endwise projecting tongue, said tonguesbeing disposed in lateral edgewise confronting relation, but spaced fromeach other, and a relatively massive body of low-melting point metalextending across and united to both said tongues and forming the soleelectrical connection between said tongues.

2. A dual-element fuse link including first and second relatively longstrips of metal each having an endwise projecting tongue, said tonguesbeing disposed in lateral edgewise confronting relation, but spaced fromeach other, and a relatively massive body of low-melting point metalextending across and united to both said tongues and forming the soleelectrical connection between said tongues, said strips havingconstricted regions adjacent to said massive body.

3. A dual-element fuse including an enclosure of insulating materialhaving a pair of terminals, a first strip of metal joined to one of saidterminals and a second strip of metal joined to the other of saidterminals, a body of relatively low-melting alloy forming the sole meansinterconnecting said strips, said strips having respective relativelythin edgewise confronting tongues of relatively large area spaced fromeach other and connected by respective metal-to-metal fused joints tosaid body of lowmelting metal and each of said strips having a portionof constricted cross-section closely adjacent to said body oflow-melting alloy and remote from said terminals.

4. A dual-element fuse including an enclosure of insulating materialhaving a pair of terminals and a transparent closure forming a window,and a fuse link connected to said terminals respectively, said fuse linkincluding two relatively long strips of metal each having an endwiseprojecting tongue and said tongues being spaced apart and being disposedlaterally opposite each other edgewise, and a relatively massive body ofrelatively low-melting alloy united to both said tongues and forming thesole bridging connection between them, said body being disposed closelyadjacent to said window.

5. A dual-element plug fuse including a screw-type body havingrespective end and lateral terminals, a transparent window at the end ofsaid body remote from said end terminal, and a dual-element fuse linkinterconnecting said terminals and having respective strips ofhighmelting-point metal joined to said terminals, each of said stripshaving an integral endwise-projecting tongue, said tongues being inedgewise laterally confronting relationship to each other, a relativelymassive body of lowmelting-point alloy interposed physically between butjoined to said tongues and forming the sole electrical connectionbetween said strips, at least one of said strips having a constrictedportion adjacent to said body, and said body having a fiat area bearingfuse-link rating indicia disposed adjacent to said window.

6. A dual-element fuse including a fuse link having respective strips ofhigh-melting-point metal, each of said strips having an integralendwise-projecting tongue, said tongues being in edgewise laterallyconfronting relationship to each other, a relatively massive body of lowmelting-point alloy interposed physically between but joined to saidtongues and forming the sole electrical connection between said strips,at least one of said strips having a constricted portion adjacent tosaid body, and said body having a flat area bearing fuse-link ratingindicia.

References Cited by the Examiner UNITED STATES PATENTS 713,831 11/02Badeau 200 1,122,478 12/14 Cole ZOO-423 1,426,827 8/22 Eustice 29155.51,848,757 3/32 Trumbull 200121 2,055,866 9/36 Jung et al. ZOO-1352,576,405 11/51 McAlister 29-155.5 2,727,110 12/55 Von Hoorn 2001352,747,257 5/56 Ashcroft et a1. 29-155.5 2,816,989 12/57 Sugden 200--1352,853,580 9/58 Mauerer 200-117 2,858,396 10/58 Sugden 200-13S 2,859,30711/58 Enk 200135 3,042,777 7/62 Pertici 200-123 3,089,012 5/63 Abrams200123 FOREIGN PATENTS 439,517 12/ 35 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

RICHARD M. WOOD, Examiner.

1. A DUAL-ELEMENT FUSE LINK INCLUDING FIRST AND SECOND RELATIVELY LONGSTRIPS OF METAL EACH HAVING AN ENDWISE PROJECTING TONGUE, SAID TONGUESBEING DISPOSED IN LATERAL EDGEWISE CONFRONTING RELATION, BUT SPACED FROMEACH OTHER, AND A RELATIVELY MASSIVE BODY OF LOW-MELTING POINT METALEXTENDING ACROSS AND UNITED TO BOTH SAID TONGUES AND FORMING THE SOLEELECTRICAL CONNECTION BETWEEN SAID TONGUES.